Glass fibre boats are built of resin reinforced with glass, and the resin is commonly polyester dissolved in styrene. The styrene is a monomer which, with the help of a catalyst, links (polymerises) the chains of polyester molecules into a three-dimensional structure. This is the curing process. You need enough styrene but not too much, and any little that is left over gives rise to the typical smell of a ‘fibreglass’ boat.